1. Field of the Invention
The present invention relates to a ceramic heater.
2. Description of the Related Art
The semiconductor-producing apparatus is equipped with a ceramic heater to heat wafers, which are substrates, for manufacturing semiconductor films from raw material gases such as silane gas by thermal CVD or the like.
A configuration so-called a dual zone heater is known as a ceramic heater. For the dual zone heater, an inner resistance-heating element and an outer resistance-heating element each comprising a high-melting point metal such as molybdenum are buried in a ceramic substrate. Separate current-introducing terminals are connected to the respective resistance-heating elements, and the inner resistance-heating element and the outer heating element are independently controlled by applying a given voltage to each resistance-heating element.
For example, in an application for heating semiconductor wafers, controlling the temperature throughout the heating surface uniformly is necessary, and it is a demand that strict specifications are satisfied, such as temperature differences being within xc2x15xc2x0 C. throughout the heating surface under a use condition. However, a so-called heat spot may practically occur on the heating surface. Occurrence of the heat spot tends to significantly increase when a target temperature of the beating surface is not less than 500xc2x0 C., and further not less than 600xc2x0 C. The occurrence of the heat spot may cause a variation in thickness of the semiconductor film at the heat spot.
The inventors further studied and found that when the semiconductor wafer is provided on the ceramic hearer and a semiconductor film is formed thereon, an identical pattern of the semiconductor film, for example, as a spiral resistance-heating wire buried in the substrate of the ceramic heater may appear on the semiconductor wafer. Such a pattern shows that a pattern of the heat spot is occurring on the heating surface corresponding to the pattern of the resistance-heating element by an effect of the resistance-heating element buried in the substrate.
It is an object of the present invention to provide a ceramic heater comprising a ceramic substrate having a heating surface for supporting and heating an object to be processed, a heating element provided in the substrate, and embossed portions on the heating surface which are to contact with the object thereby preventing an adverse effect on the object caused by a heat spot on the hearing surface.
The present Invention relates to a ceramic heater including a ceramic substrate having a heating surface for supporting and heating an object to be processed, a heating element provided in the substrate, and embossed portions on the heating surface which are to contact the object. A heat spot having a relatively high surface temperature will exist on the heating surface when an average temperature of the heating surface is raised to reach a target temperature and the number of the embossed portions per unit area on the heat spot is less than that on the rest of the heating surface,
The present invention also relates to a ceramic heater including a ceramic substrate having a heating surface for supporting and hearing an object to be processed, a heating element provided in the substrate, and embossed portions on the heating surface which are to contact with the object. The heating element is buried in a planar form in the substrate and when the heating element is projected on the heating surface In a direction perpendicular to the hearing surface, the number of the embossed portions per unit area on the projected heating element is less than that on the rest of the heating surface.
The present invention further relates to a ceramic beater including a ceramic substrate having a heating surface for supporting and heating an object to be processed, and a heating element provided in the substrate, wherein a hollow space is provided between the heating surface and the heating element in the substrate and a plurality of heat conductors are provided in the space to transverse the space.
A form of placing the heating element in the substrate is not restricted. Preferably, the heating element is buried in the substrate, but it can be provided on the surface of the substrate opposed to the heating surface.